1. Field of the Invention
This invention relates to a composition formed preponderantly of a polyborosiloxane and used for the production of an electrically insulating layer and to an enameled wire using the composition.
2. Description of the Prior Art
Polyborosiloxanes which have the main claim of boron, silicon and oxygen have been known as semi-inorganic polymers.
These polyborosiloxanes include a compound obtained by the reaction of boric acid, a derivative thereof, and phenylsilane (U.S. Pat. No. 4,152,509) and a compound produced by the reaction of dichlorosilane with an aliphatic alcohol, an aromatic alcohol, a phenol, or an aromatic carboxylic acid (U.S. Pat. No. 4,342,487). And a method which comprises coating the surface of a metallic substrate with such a polyborosiloxane and subjecting the formed layer to a thermal treatment (U.S. Pat. No. 4,267,210) has been also known to the art.
These known polyborosiloxanes invariably are hardly soluble in solvents capable of being baked, fail to form layers on metallic surfaces after they are baked and, if allowed to form layers, the layers are deficient in flexibility and intimate adhesiveness to metallic surfaces. Thus, they fall short of effectively serving as electrically insulating coating compositions. In the circumstance, no electrically insulating layer using a semi-inorganic polymer has ever been materialized.